In a lighting device for a vehicle, a semiconductor light emitting device such as an LED (Light Emitting Diode) is used for a light source. A lighting control circuit for controlling operation of the LED is mounted on the lighting device for a vehicle of this type.
Some lighting control circuits use a switching regulator to control an output voltage for the LED based on the current of the LED. The switching regulator controls the output voltage so as to cause a specified current to flow to each LED regardless of whether the LEDs are connected in series to, or in parallel with, the switching regulator.
In some cases in which an output of the switching regulator is short-circuited or grounded, however, a load of the switching regulator is increased so that a failure is caused with an excessive power burden. Referring to a switching regulator of a flyback type, for example, in some cases in which the output of the switching regulator is opened as the result of a disconnection, an output voltage becomes too high.
Therefore, it has been proposed that the output voltage of the switching regulator be dropped when an abnormality on the output side of the switching regulator is detected (see, e.g., Japanese Patent Document JP-A-2004-134147).
When the output terminal of the switching regulator generates a ground fault, the abnormality is generated on the output side of the switching regulator. Even if the ground fault is generated in any of the portions between the LEDs, however, the ground fault cannot be detected.
More specifically, is has been suggested to set a whole LED block as a load of the switching regulator and to reduce the output voltage of the switching regulator when an abnormality is generated over the whole LED block. However, even if the ground fault is generated in any of the portions between the LEDs, therefore, the ground fault cannot be detected.